The present invention relates in general to methods and apparatus for forming deep cast-in-place concrete piles, and more particularly to methods and apparatus for forming cast-in-place concrete piles driven into the ground for greater depth than average piles, for example, in excess of 100 feet, by driving a hollow metallic pipe pile member having a height corresponding to about half the design depth of the completed pile into the ground for substantially the full depth of the pipe pile member and then assembling a hollow tubular driving mandrel to the top of the pipe pile member and driving the mandrel and pipe pile member assembled therewith to drive the pipe pile member to the design depth, in association with a transportable fill hopper by which flowable concrete is gravity fed about and into the mandrel to fill the pipe pile section and mandrel section during driving of the mandrel and thereby form a monolithic concrete cast-in-place pile.
For a long time, cast-in-place concrete piles of the type wherein a steel shell or outer casing was driven in the ground to be permanently left in the ground and concrete was thereafter poured into the steel shell to form the pile, found widespread utility in the construction field. However, because of the cost and shortage of steel, delays in securing delivery of steel casings, and related factors, efforts have been made for many years to devise effective methods of providing cast-in-place concrete piles which do not require a steel shell. Cast-in-place concrete piles which do not have such steel shells are generally termed caseless piles. The advantage to be gained by such cast-in-place caseless concrete piles lie principally in the reduction in material costs achieved by elimination of the steel shell, which is consumed in driving each pile and would not be recoverable, and avoidance of scheduling problems arising from slow steel deliveries.
One known procedure for forming caseless concrete piles which has enjoyed some success, which was devised to avoid the problems inherent in the use of cased piles, involved advancing into the soil some type of pile tip, driving foot, or boot member, achieved, for example, by use of an elongated hollow tubular driving mandrel to which the driving tip is releasably assembled, and with the use of a conventional pile driving rig, driving the mandrel and pile tip into the ground to the desired depth while continuously providing an adequate supply of flowable concrete around or within the mandrel so that the concrete can flow or be directed into the ground cavity being formed by the driving tip and mandrel. In practice, the elongated hollow tubular driving mandrel has a plurality of spaced openings in the mandrel wall through which the concrete can flow into the hollow interior of the mandrel and some type of receptacle or hopper device for containing the concrete prior to its descent into the cavity being formed by the driving tip and mandrel assembly, and for preventing unnecessary spillage, is associated with the mandrel to achieve gravity flow of the flowable concrete in the hopper into the cavity being formed by the mandrel and driving tip. The fill hoppers used in practicing this method have usually embodied shapes wherein downwardly converging planes or curvilinear surfaces are formed around the driving mandrel, and a bottom discharge hole which is only slightly larger than the diameter of the driving mandrel is provided at the bottom of the receptacle defined by the fill hopper through which the mandrel passes, so that the fill material such as flowable concrete can flow downwardly about the outer surface of the mandrel into the cavity being formed and can also flow through the holes in the mandrel wall into the interior of the mandrel. The mandrel, of course, is withdrawn from the ground after the mandrel and driving tip have been driven to the design depth for the pile, and the mandrel and hopper can then be moved to another pile site and reused with another driving tip for each additional pile to be formed.
A problem which has been encountered in putting this cast-in-place caseless pile forming method into practice has been in providing caseless concrete piles for projects requiring pile foundations with piles having a length much greater than normal pile lengths, such, for example, as projects having piles of an average length of about 120 feet or longer. Forming a cast-in-place caseless concrete pile with the mandrel and hopper equipment described above would encounter great difficulties in properly forming piles at such extreme depths, while the use of the conventional pipe pile forming methods would involve use of extremely long pipe pile sections and consume very large quantities of steel leading to great foundation costs and would require welding of pipe sections together to form the long pipe piles which introduces significant additional cost.
An object of the present invention is the provision of a novel method and apparatus for producing very deep cast-in-place concrete piles wherein a tubular metallic pile sheel or pipe having a length corresponding to a significant fraction of the total design pile length is first driven into the ground for approximately its full length and then a caseless-pile-forming mandrel is assembled thereto and positioned relative to a fill hopper to drive the assembled tubular shell and mandrel the remaining distance required to form the deep pile while gravity flowing concrete from the hopper into the mandrel and the assembled tubular shell sections to fill the same with concrete, and thereafter withdraw the mandrel, leaving a monolithic deep cast-in-place concrete pile with the lower portion thereof encased in a metallic pile shell.
Another object of the present invention is the provision of a novel method and apparatus for forming a deep cast-in-place pile wherein the pile is formed of monolithic concrete throughout its full height with the approximate lower half thereof encased in a metallic pipe or shell permitting economical and efficient formation of the deep pile beyond depths for which cast-in-place caseless concrete piles are suitable.
Other objects, advantages and capacilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.